1. Field of the Invention
The present invention relates to an optical recording medium for storing a high-density of data and a method of recording data on the optical recording medium.
2. Description of the Related Art
In general, data are read and recorded on an optical recording medium by an optical pickup device using a non-contact method. Types of optical recording media include a compact disc (CD) and a digital versatile disc (DVD). These optical recording media are distinguishable by data recording capacity, although a diameter and a thickness of each of the recording media are the same at 12 cm and 1.2 mm, respectively. Thus, an external structure of the CD and the DVD are the same.
The data recording capacity of the DVD is larger than the data recording capacity of the CD even though the appearance and size of the DVD are the same as the appearance and size of the CD. This is achieved by internal features of the DVD which are different from internal features of the CD. The different internal features include a data recording standard, a thickness of a substrate on which data are recorded, a track pitch, and a minimum size of a pit.
The standard for recording data onto a DVD is stricter than the standard for recording data onto a CD and a wavelength of a light source for reading and recording data is shorter for the DVD than for the CD.
As an amount of data to be recorded on a recording medium increases due to an emergence of a new information transmission medium, for example, high-definition (HD) TV, increased data recording capacity is required of the DVD. To meet this requirement, a DVD having increased data recording capacity has emerged, for example, a DVD having a plurality of recording surfaces.
In detail, FIGS. 1A, 1B and 1C show a DVD according to prior art which includes first and second information substrates 111 and 121, on which information signals are recorded on surfaces of each of the substrates 111 and 121, and a third information substrate 131, arranged between the first information substrate 111 and the second information substrate 121, on which information signals are recorded on both surfaces of the substrate 131. The first information substrate 111 includes a first incident surface 111a through which light L for recording/reproducing is transmitted and a first recording surface 111b on which an information signal is recorded. A first reflective layer 113, which reflects some incident light and transmits a remainder of the incident light, is formed on the first recording surface 111b. A first recording layer 115 on which an information signal is recorded and a second reflective layer 117, which is formed on the first recording layer 115 and reflects some of the incident light, are formed on the first reflective layer 113.
A second information substrate 121 includes a second incident surface 121a through which the light L for recording/reproducing is transmitted and a second recording surface 121b on which an information signal is recorded. A third reflective layer 123 which reflects some of the incident light is formed on the second recording surface 121b. A second recording layer 125 on which an information signal is recorded and a fourth reflective layer 127, which is formed on the second recording layer 125 and reflects some of the incident light, are formed on the third reflective layer 123.
A third information substrate 131 is bonded to and formed between the second reflective layer 117 and the fourth reflective layer 127. The third information substrate 131 includes a third recording surface 131a on which an information signal is recorded/reproduced by light transmitted through the first and second reflective layers 113 and 117, and includes a fourth recording surface 131b on which an information signal is recorded/reproduced by light transmitted through the third and fourth reflective layers 123 and 127.
In this way, in a case where two or more data recording surfaces are sequentially formed on a surface, assuming that the data recording surfaces are represented as L0, L1, L2, . . . LN in order starting with the data recording surface closest to the light source, a laser for recording or reading must be transmitted through L0 when data are to be recorded on L1 or when data recorded on L1 are read. The laser for recording or reading may be influenced by the physical structure of L0, for example, a pit, a groove, or a groove having a mark as a data recording. For example, as the laser is diffracted by the physical structure of L0 which is in the path of the laser, the strength of the laser reaching L1 is thereby varied. As a result, the quantity of light reflected from L1 is different from the quantity of light reflected where the laser is not diffracted, and reading data recorded on L1 correctly becomes impossible. Also, in a case where the laser is used for recording, the intensity of the laser after passing through L0 is lower than a critical intensity required for recording. As a result, data may not be recorded correctly, or data, which are different from original data (incorrect data), may be recorded.